Astronomers examine 6.1 million stars for alien radio signals

A search for extraterrestrial intelligence across the Milky Way surveyed more than 6.1 million stars, vastly exceeding prior astronomical estimates for existing radio sweeps. Researchers monitoring galactic space often contrast negative detection results against the approximately 100 billion stars present within the galaxy.

Louisa Mason, a doctoral researcher at the University of Manchester, determined that past observational sweeps encompassed far more stellar targets than astronomers previously recognized. She reached this conclusion by testing sky data against the Besançon Galactic Model to simulate stellar distributions. By applying the Besançon Galactic Model to evaluate data collected during 1,327 sky scans by the Green Bank and Parkes radio telescopes, Mason revealed that the instruments surveyed more than 6.1 million stars rather than the 288,315 targets cataloged originally. Most of those additional bodies remained unlisted because of their faint visual output.

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“One of the most exciting things about this work is realizing that we’ve surveyed many more stars than initially thought,” Mason said. “Even a very small observation can contain a huge number and diversity of stars that we might never have intended to study.” Mason noted that the absence of a detection should not discourage observers.

Commensal SETI operations capture background stellar emissions whenever a radio telescope points toward a primary target star to record routine scientific observations.

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Astronomers typically calculate the stellar population inside a telescope beam by consulting comprehensive records compiled by the European Space Agency Gaia mission. These registries catalog luminous stars while omitting dimmer bodies invisible to optical and infrared instruments. Radio antennas nevertheless capture potential technosignatures from those uncataloged coordinates.

Listening efforts remain constrained by limited time allocations per target and narrow frequency coverages that permit intermittent transmissions to pass undetected. Radio detections require precise timing.

Researchers began modern SETI initiatives in 1960 with a focus on an electromagnetic span designated as the water hole. This specific window extends from the 1,420 MHz atomic hydrogen line to the 1,666 MHz hydroxyl emission band. Hydrogen and hydroxyl combine chemically to create water. The name of the region derives directly from that chemical association.

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The terrestrial atmosphere does not absorb radio signals across this quiet band, enabling ground receivers to operate efficiently. Standard astronomical programs also survey hydrogen frequencies continuously, creating frequent opportunities for incidental signal discoveries. Transmitting civilizations might likewise favor the channel because of the shared physical importance of water.

Mason directed the Atacama Large Millimeter/submillimeter Array in Chile to carry out the first extraterrestrial intelligence survey utilizing that facility.

“For decades, SETI researchers have concentrated on a relatively small part of the radio spectrum,” Mason said regarding the exploratory search. “We wanted to ask what might happen if we looked somewhere very different.”